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I have two LED strips powered via two dimmers, like so:

Current setup

Certain combinations of dimming on both dimmers lead to the LED strips blinking. The level of blinking is not deep, maybe 15-20% of brightness, but very annoying nevertheless. The frequency of blinking can be changed by finely adjusting the levels on dimmers. These are not fixed values; several combinations lead to blinking.

Nothing is overheating. The dimmers are rated at 8A each; max total consumption from the power supply is about 7A at 12V. Connectors and wires are fine.

If I turn off either dimmer, the other never produces blinking, at any level.

What might be the cause of this?

It looks very much like interference. My idea is that the dimmers, being PWMs, consume power in impulses. I suspect that the frequency of the PWM varies slightly with power. So two PWMs with slightly different frequencies can produce a wobble frequency in power consumption which the power supply fails to compensate. (I can be totally wrong, of course.)

How can I get rid of that?

(1) My idea is to add a large capacitor (e.g. 500µF) before both dimmers, to help level the input voltage:

Input capacitor

(2) My other idea, in case I got the cause all wrong, is to add capacitors to the LED strip inputs, so that pulses from the dimmers are leveled:

enter image description here

Does this make sense? One of my concerns is the large charging current of the capacitors; the power supply and the dimmers have short-circuit protection, though.

Any advice is appreciated.

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My idea is that the dimmers, being PWMs, consume power in impulses.

Yes

I suspect that the frequency of the PWM varies slightly with power.

Unlikely. They're microcontrollers, their clock either comes from a quartz or a RC oscillator on the chip which would depend on power supply voltage but there's a 3V3 or 5V regulator in there so it should be stable.

But even if the frequencies don't change, your two dimmers will have slightly different frequency due to component tolerance, so your original idea still holds:

So two PWMs with slightly different frequencies can produce a wobble frequency in power consumption which the power supply fails to compensate.

Yes, and that's probably the cause. It shouldn't happen since the power supply is rated for "10A" and your LED strips draw 7A when fully on, but that depends on the quality of the power supply... if it's cheap, who knows.

option 2 in your answer: Do not put capacitors in parallel with the LED strips: a cap after the PWM switch would draw large pulsed current every time the PWM switch turns on.

option 1 in your answer: Yes you should try putting a large cap just at the output of the power supply. It should be low-ESR, which means either a high value general purpose cap like 4700µF or more, or a special low-ESR cap.

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